Preparation of polyphenyl by pyrolysis of aromatic hydrocarbons



United States Patent Ofitice Patented Jan. 11, 1966 This invention relates to pyrolysis, and particularly to the pyrolysis of aromatic hydrocarbons to biphenyl and polyphenyl.

Pyrolytic processes for converting benzene and other aromatic hydrocarbons into biphenyl and polyphenyls are well known. These processes normally involve vaporizing benzene, heating the vapors to pyrolyzing temperatures, and subsequently separating the product from the unconverted feed material. The reaction is usually executed in industrial installations by passing the hydrocarbon vapors through tubes, conduits, or passageways which are externally heated to pyrolytic temperatures. The apparatus employed in such operations generally includes a hydrocarbon vaporizer together with one or more pyrolyzing tubes or passageways extending from the vaporizer to a suitable condenser or other conventional means in which the product is separated from the more volatile starting hydrocarbon. Any suitable heat source can be used to provide the requisite temperature for the vaporizer and pyrolysis tubes.

While pyrolytic methods have enjoyed commercial acceptance, such processes have been plagued with one major difficulty. That is the formation and deposition of carbon or coke in the pyrolyzing apparatus. The coke formation results from the decomposition of the hydrocarbon feed at the high temperatures required, and, prior to the present invention, was generally considered to be an inherent shortcoming of such chemical transformations. The carbon is usually formed in and deposited on the pyrolytic tubes in which the highest temperatures are encountered. Thus the effective diameter of the tubes is progressively reduced, and the tubes ultimately clogged. This requires halting the operation and dismantling the apparatus to ream the carbon from the passageways. In addition, the efficiency of the process was impaired due to the difficulty in effecting adequate heat transfer through the carbon depositions. In the past, various attempts have been made to avoid such coking and the difliculties associated therewith.

These previously known methods involve the use of additives in the hydrocarbon feed, precise control of operating conditions, increased linear velocity in small diameter tubes, and numerous materials in the construction of the reactor. The materials heretofore used to provide a hot surface in contact with the hydrocarbon vapors include carbon, graphite, Nichrome, stainless steels, nitrided and carbide coated iron, as well as iron coated with a sulfide or with various other metals. Although the carbon formation problem has been attacked in a number of ways,

the previously described solutions have, at best, met with only a modicum of success. Thus, prior to the advent of the present invention, all commercial pyrolytic methods involved considerable coking which reduces efiiciency and involves frequent shutdown for carbon removal.

Therefore, it is an object of the present invention to provide a new and novel method and apparatus for the pyrolysis of aromatic hydrocarbons, overcoming the disadvantages of the prior art. A more specific object is to provide a benzene pyrolysis method and apparatus in which carbon formation is reduced to an absolute minimum.

These and other objects are accomplished in accordance with the present invention, generally speaking, by pyrolyzing benzene or other aromatic hydrocarbon vapors to biphenyl and/or polyphenyls in apparatus having vaporcontacting surfaces which inhibit and minimize coke formation and deposition. More specifically, the invention contemplates heating benzene or other aromatic hydrocarbons above their boiling points, heating the resulting vapors to pyrolyzing temperatures while passing through a tube, conduit or passageway having inner surfaces which inhibit carbon formation, and subsequently separating the pyrolytic products from the unconverted hydrocarbon starting material. It has now been found that carbon formation in the pyrolysis of benzene and other aromatic hydrocarbons to biphenyl and polyphenyls is substantially eliminated or reduced to an insignificant mainimum when the aromatic vapors, at pyrolyzing temperatures, are confined by metallic alloys having the following approximate composition range:

Percent Cobalt 0.5 to 2.5 Chromium 20.5 to 23 Molybdenum 8 to 10 Tungsten 0.2 to 1 Iron 17 to 20 Carbon 0.05 to 0.2 Silicon Up to 1 Manganese Up to 1 Nickel Balance Optimum results are obtained by employing an alloy of the above type in which the various components are present in about the following approximate proportions: 1.5% cobalt, 22% chromium, 9% molybdenum, 0.6% tungsten, 18% iron, 0.1% carbon, up to 1% silicon, up to 1% manganese, and the balance (about 47.3%) nickel. Alloys of this type are commercially available under the trade name Hastalloy X from the Haynes Stellite Company, a division of Union Carbide Corporation.

Pyrolytic conversions are normally conducted on aromatic hydrocarbons in the vapor state under a gauge pressure between about 10 and about 200 pounds per square inch and at temperatures between about 600 C. and 950 C. The rate of conversion is uneconomically slow at temperatures less than about 600 C., where-as excessive degradation occurs at temperatures above about 950 C. In accordance with the present invention, benzene is vaporized and the vapors heated to a temperature of approximately 600 C. by any conventional means. The heated vapors are then passed into contact with pyrolytic elements, preferably tubes, of the above alloys maintained between about 600 C. and 950 C. The vapors are then cooled below about 600 C., and the biphenyl or polyphenyls separated from the unconverted hydrocarbon feed by condensation. Alternately, the pyrolysis is carried out in a single reaction zone without a separate preheating zone. The rate of conversion generally varies between about 5% and about 30%, and higher, based primarily on the pressures and temperatures employed. The unconverted feed material is then recycled, together with reaction initiators and other add-itives, it so desired.

In carrying out the present invention, the formation of carbon is minimized or substantially eliminated by restricting the aromatic hydrocarbon vapors at pyrolyzing temperatures to contact with the above-described alloys. The pyrolytic tubes can be merely lined with the alloy. However, in order to avoid the possibility of thernally-induced stresses in the tubular walls, it is preferred to use these alloys exclusively in the construe of the pyrolytic tubes or conduits. The advantages of the invention are most fully realized by using pyrolytic tubes lined throughout their entire length with the above-described nickel-base alloys. It will be appreciated, however, that these advantages can be achieved in proportionately lesser degrees by utilizing other materials in portions of the tube length. 7 p

The apparatus employed in accordance with the pres.- ent invention includes a hydrocarbon vaporizer, a pyrolyzing element or tube of the specified nickel-base alloys,;and product-collecting means such as a condenser. These units are provided with suitable connecting means to permit. fluid flow from the vaporizer through the pyrolyzin g element into the condenser. Any conventional means may be employed to obtain the proper operating temperatu'res throughout theapparatus. One or more pyrolytic tubes can be incorporated into the present apparatus, the size and number of the tubes depending upon the relative size of the vaporizer and upon the rate of production desired. The pyrolytic conduits are preferably tubular, but can assume any'convenient cross-sectional configuration. The pyrolyzing tubes are generally straight; but they can also follow curved, tortuous or helical paths provided that the flowgof the vapor stream is not impede-:L' A. recycle circuit is also normally provided to conduct the unconverted hydrocarbon feed from the condenser to the vaporizer.

The invention will be more fully understood by reference to the following detailed description of preferred embodiments thereof. In these examples and throughout the specification, all properties are expressed in parts by Weight unles otherwise specified.

In accordance with this example, benzene was vaporized at the .rate of about 35 cc. per minute, the vapors heated to about pyrolyzing temperature and passed through a horizontally extending tube of an alloy containing about 1.5% cobalt, 22% chromium, 9% molybdenum, 0.6% tungsten, 18% iron, 0.1% carbon, 0.75% silicon, 0.75 manganese, and the balance nickel. The tube, which was substantially straight, had an internal diameter of about three-ei'ghths inch and a length of about three feet, and was maintained at a temperature between-about 730 C. to about 800 'C. by means of an electric furnace. The material from the tube was com den'sed to separate the resultant biphenyl from the unconverted benzene, which was recycled. During the process, the pressure within the vaporizer and the tube was maintained at a gauge pressure of approximately 40 pounds per square inch. With these conditions, well over 10% of the benzene passing through the system was about 16 /2 hours, and then stopped to permit inspection of the tube. Only a faint trace of non-adherent dust This insignificant amount ofpyrolytic cone converted to biphenyl. The operation was continued for I p base alloy. The commercially available stainless steels used and their nominal compositions are tabulated below.

Type No 302B 309 310 '0. 0. 20 0. 2. .2. 0 2. 0 2. 0-3. 1. O0 1. 17. 0-19. 0 22. 0-24. 0 24. 0-20. 0 8. 0-10. 0 12-0. 15. 0 10. 0-22. 0 Balance Balance Balance The tube formed of No. 309 stainless steel was subject to severe coking and carbon deposition after benzene vapor's were passed through it at atemperature ranging between about 730 C. and about 800 C. for a period of about 16 /2 hours. At the end of this time, a considerable amount of coke had been deposited throughout the length of the tube, and the effective diameter of the tube was reduced to substantially capillary proportions. Upon visual observation, only a pinhole of light could be seen through the tube. Similarly unsatisfactory results were obtained with a'tube of No. 310 stainless steel subjected to the same operating conditions for about 16 /2 hours. A benzene pyrolysis at about 800 C.using a No. 302B stainless steel tube resulted in the tube being substantially blocked with a porous coke throughout its length after a 40-hour run. The results of these tests, using the abovedescribed nickel-base alloys and stainless steels of the prior art, are summarized in the following table.

The advantages of the nickel-base alloy tubes of the present invention over stainless steel tubes are graphically portrayed in the above table. Although stainless steel had been recognized as superior material for the construction of pyrolytic apparatus, this utilization does not result in the achievement of the objects of the present invention.

The term polyphony is used herein in its broadest sense to designate polymerized benzene or substituted benzenes. Thus it encompasses'biphenyl, terphenyls, quaterphenyls, alkyl-substituted polyphenyls, phenyl-substituted naphthalenes, and the like.

Although the invention has been described in'co'nsider able detail in the foregoing for the purpose of illustration,

' it is to be understood that such' detail is solely for that purpics was conducted while maintaining the nickel-base alloy tube at a temperature of about 730 C. In this example, a conversion rate in excess of 10% was achieved for over 80 hours. At that time, the process was halted and the pyrolytic tube inspected. During this extended period of time, the only carbon deposition noted was in the. form of an exceedingly thin film lining the inner surface of the tube. This film had no measurable adverse effects on the ease of operationor onthe rate of conversion. 0

I In order to provide a basis of comparisomthe above,

pyrolytic processes were substantially repeated using stainless steel tubes instead of a tube of the specified nickelpose and that many modifications can be made without departing from the spirit and scope of the invention.

The embodiments of the invention in which an exclusive property or privilegeis claimed are defined as follows:

1. A method of pyrolyzing aromatichydrocarbons to polyphenols which comprises .passing a stream of hydro.- c-arbon vapors at .p'yrolyzing temperatures through a zone lined with a nickel-base alloy consistingessentially of from about 0.5% to about 2.5%.cobalt, from about 20.5% to about 23% chromium, from about 8% to about 10% molybdenum,.from about 0.2% to about 1% tungsten, from about 17% to about 20% iron, from about 0.05% tov about 0.2% carbon, up to about 1% silicon, up to about 1% manganese, and the balance nickel.

2. A method of pyrolyzing aromatic hydrocarbons which comprises maintaining hydrocarbon vapors at pyrolyzing temperatures in contact with a nickel-base alloy and removing the vapors, the nickel-base alloy consisting essentially of from about 0.5% to about 2.5% cobalt, from about 20.5% to about 23% chromium, from about 8% to about 10% molybdenum, from about 0.2% to about 1% tungsten, from about 17% to about 20% iron, from about 0.05% to about 0.2% carbon, up to about 1% silicon, up to about 1% manganese, and the balance nickel.

3. A method of pyrolyzing benzene to polyphenols which comprises vaporizing benzene, maintaining the benzene vapor at a pyrolyzing temperature in contact with a nickel-base alloy, and removing the vapor, the nickel-base alloy consisting essentially of from about 0.5% to about 2.5% cobalt, from about 20.5 to about 23% chromium, from about 8% to about 10% molybdenum, from about 0.2% to about 1% tungsten, from about 17% to about 20% iron, from about 0.05% to about 0.2% carbon, up to about 1% silicon, up to about 1% manganese, and the balance nickel.

4. A method of pyrolyzing benzene to biphenyl which comprises vaporizing benzene, maintaining the benzene vapor at a temperature between about 600 C. and about 950 C. While passing through a zone of nickel-base alloy, and removing the vapor from the zone, the nickel-base alloy consisting essentially of about 1.5% cobalt, about 22% chromium, about 9% molybdenum, about 0.6% tungsten, about 18% iron, about 0.1% carbon, about 1% silicon and manganese, respectively, and the balance nickel.

5. A method of pyrolyzing benzene to biphenyl which comprises passing a stream of benzene vapors at pyrolyzing temperatures through a zone lined with a nickel-base alloy consisting essentially of about 1.5% cobalt, about 22% chromium, about 9% molybdenum, about 0.6% tungsten, about 18% iron, about 0.1% carbon, about 1% silicon and manganese, respectively, and the balance nickel.

References Cited by the Examiner UNITED STATES PATENTS 1,968,154 7/1-9'34 Moose et a1. 260-670 1,978,069 10/1934 Williams 260-670 2,099,350 11/1937 Stoesser 260-670 2,208,517 7/1940 Prutton 260-670 2,744,010 5/1956 Callaway 75171 2,765,226 10/1956 Nisbet 75171 DELBERT E. GANTZ, Primary Examiner.

DANIEL E. WYMAN, ALPHONSO D. SULLIVAN,

Examiners. 

1. A METHOD OF PYROLYZING AROMATIC HYDROCARBONS TO POLYPHENOLS WHICH COMPRISES PASSING A STREAM OF HYDROCARBON VAPORS AT PYROLYZING TEMPERATURES THROUGH A ZONE LINED WITH A NICKEL-BASE ALLOY CONSISTING ESSENTIALLY OF FROM ABOUT 0.5% TO ABOUT 2.5% COBALT, FROM ABOUT 20.5% TO ABOUT 23% CHROMIUM, FROM ABOUT 8% TO ABOUT 10% MOLYBDENUM, FROM ABOUT 0.2% TO ABOUT 1%TUNGSTEN, FROM ABOUT 17% TO ABOUT 20% IRON, FROM ABOUT 0.05% TO ABOUT 0.2% CARBON, UP TO ABOUT 1% SILICON, UP TO ABOUT 1% MANGANESE, AND THE BALANCE NICKEL. 